Roll dart_style 1.3.9 into repo.

This does not affect the formatting of any existing code, so is safe to
roll without updating the pre-built SDK.

Change-Id: I2e7fc20d6933d136dc0390f93f6bc72dc340e9ba
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/170141
Auto-Submit: Bob Nystrom <rnystrom@google.com>
Commit-Queue: Nate Bosch <nbosch@google.com>
Reviewed-by: Nate Bosch <nbosch@google.com>

Author: munificent

CHANGELOG.md

@@ -39,6 +39,11 @@ opted out of null safety by adding `// @dart=2.9` to the beginning of the file.
   `--enable-assert-initializers` command line options. These options haven't
   been supported in a while and were no-ops.
 
+#### dartfmt
+
+* Don't duplicate comments on chained if elements.
+* Preserve `?` in initializing formal function-typed parameters.
+
 #### Linter
 
 Updated the Linter to `0.1.122`, which includes:

DEPS

@@ -98,7 +98,7 @@ vars = {
   #     and land the review.
   #
   # For more details, see https://github.com/dart-lang/sdk/issues/30164
-"dart_style_tag": "1.3.8+1",  # Please see the note above before updating.
+"dart_style_tag": "1.3.9",  # Please see the note above before updating.
 
   "chromedriver_tag": "83.0.4103.39",
   "dartdoc_rev" : "72c69f8659ce8823ce2dde9a4f758b0fa617ab5e",